This invention relates to improvements in a cylinder control device of a hydraulic cylinder apparatus capable of doing work of high magnitude.
In a hydraulic cylinder apparatus, the work done by a piston is given by the product of the working stroke of the piston, the effective pressure bearing area of the piston and the pressure of fluid acting on the piston. In a known hydraulic cylinder apparatus, difficulties have been encountered in maintaining the pressure in a working chamber defined by the piston and the cylinder body at a high level during the entire stroke of the piston, and thus it has been difficult to cause the piston to perform work of a high magnitude. Since the effective fluid pressure in the working chamber is produced by the load applied to the piston, the effective fluid pressure may be only produced near the dead point in the case of a hydraulic cylinder apparatus of the type wherein a load is applied to the piston near its dead point. Thus it is particularly difficult to cause a pressure of high level to be produced in the working chamber through the entire stroke of the piston in the case of the hydraulic cylinder apparatus of the aforesaid type.
In view of the foregoing, proposal has hitherto been made (Japanese Patent Application No. 53-93009, filed July 29, 1978) to use a cylinder control device which is capable of increasing the internal pressure of the working fluid chamber in the cylinder body above the internal pressures of the devices of the prior art, so as to enable the hydraulic cylinder to do work of a higher magnitude than has hitherto been done.
This invention is directed to a modification of the cylinder control device that has been proposed as described hereinbefore.